Grab the notes sheet from back lab table… Objectives: Describe Meiosis and the formation of sex cells. Compare your vocab definitions to the notes.

Chapter Meiosis

Asexual Reproduction - Asexual reproduction involves body cells: New organisms are produced from one parent (they are identical) 2 Types of cells in body: Somatic cells: body cells Gametes: sex cells – sperm & eggs

Sexual Reproduction - a new organism is produced when sex cells from two parents combine Sex Cells sperm: small w/ whiplike tails and heads that are almost all nucleus

Egg: usually large and contain food material Production of Sex Cells formed during meiosis During meiosis, the number of chromosomes is reduced by one-half

Example: a human body cell has 46 chromosomes or 23 pairs -during meiosis, this number is reduced to 23 chromosomes -An egg or a sperm cell has 23 chromosomes Why would the sex cells only have 23 chromosomes?

Importance of Sex Cells Diploid -a body cell w/23 pairs of chromosomes is diploid (2n) (2 of every kind of chromosome) -body cells receive one from mother and one from father during fertilization

Haploid - a sex cell w/23 chromosomes (1n) Fertilization: the joining of an egg (haploid) and a sperm (haploid) Zygote: fertilized egg (2N)

--meiosis and fertilization keep the species number of chromosomes from changing

Describe what you see…

Meiosis two divisions of the nucleus (meiosis I and meiosis II) Before the cell enters meiosis I, the chromosomes and DNA both duplicate

Overview: Meiosis I Duplicated chromosomes are separated Each chromosome still has double the amount of DNA Cytoplasm divides and forms two cells

Meiosis I 1.Prophase I: DNA coils to form chromosomes -Spindle fibers appear, nucleolus & nuclear membrane disappear -Chromosomes begin lining up w/ their homologues Synapsis: pairing of homologous chromosomes; doesn’t occur in mitosis

Crossing-over: portions of chromatids break off & reattach to adjacent chromatids on homologous chromosome Tetrad: each pair of homologous chromosomes; 4 chromatids -Orient themselves so corresponding genes are adjacent to each other

- Results in genetic recombination: New mixture of genetic material -source of variety in populations Crossing-over

2.Metaphase I: tetrads line up randomly along middle of cell - Spindle fibers from the poles attach to centromere of each homologue - The chromosomes line up 2 by 2, unlike in mitosis

3.Anaphase I: each homologous chromosome moves toward opposite pole of cell; tetrad splits -Each homologous chromosome consists of 2 chromatids attached at centromere

4.Telophase I & Cytokinesis I: -Chromosomes reach poles & cytokinesis begins -Produces 2 cells, each w/ 1 chromosome from each homologous pair

NOTE: The two cells produced by meiosis I have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I.

INTERKINESIS—rest period between Meiosis I and II; not all cells “rest”; some proceed immediately to Meiosis II

Overview: Meiosis II The amount of DNA is reduced Each new nucleus will contain only half the number of chromosomes w/half the DNA that was present at the start Cytoplasm divides resulting in 4 daughter cells

Meiosis II -DNA does NOT copy again! 5.Prophase II: spindle fibers form & begin to move chromosomes toward the middle of cell - Nuclear membrane will break down again if it formed after telophase I

6. Metaphase II: chromosomes in middle of cell 7.Anaphase II: chromatids separate & move toward opposite poles of cell 8. Telophase II & Cytokinesis II: nuclear membrane forms around the chromosomes - Cytoplasm divides, resulting in 4 new cells

Metaphase II Anaphase II Telophase II & Cytokinesis II

Gamete Formation Males: sperm is produced

In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction.

HOMEWORK: Compare your vocab definitions to the notes. We will be using this information tomorrow!!

Objectives for today: Describe the vocab definitions! Compare and Contrast Haploid to Diploid VOCAB QUIZ TOMORROW!!

Let’s see what you remember! 1.Meiosis starts out with 1 diploid cell and ends with ________________. 2.Meiosis cuts the number of chromosomes in __________. 3.When does Crossing Over occur? 4.If an alligators haploid cell has 16 chromosomes, how many does a diploid cell have? 32

On a scratch piece of paper write if this cell is diploid or haploid and how many chromosomes it contains Bone cell- Liver cell- Egg cell- Muscle cell- Sperm cell- If a pea plant’s diploid cell has 14 chromosomes, how many does a pea plant sex cell have? If an alligators haploid cell has 16 chromosomes, how many does a diploid cell have? Frog Haploid:8 Diploid: Kangaroo Haploid: Diploid: 12

Get with a partner and using your book and notes, draw/label the steps of meiosis I and II.

Meiosis Starts Draw this graphic organizer on a sheet of paper. Write the number of Chromosomes each cell has in each circle. Draw a vertical line showing where the first division happens. Draw a vertical line showing where the second division happens… Meiosis I Meiosis II

Comparing Mitosis and Meiosis Mitosis: produces 2 genetically identical diploid cells. Meiosis: produces 4 genetically different haploid cells; also different from each other